Transferrin (TF) is a serum protein synthesized in the liver that transports iron from sites of absorption to the sites of utilization. Iron-laden transferrin binds to cell surface receptors and is internalized. High levels of TF-R are expressed by actively growing normal cells, by their malignant counterparts, and by stimulated lymphocytes. Since oral epithelium divides continuously to replace the cells lost at the surface, it is reasonable to assume that TF-R would be expressed on epithelial cells of oral mucosa. However, to date this assumption has not been evaluated. While the literature reports a positive relationship between the expression of TF-R, tumor proliferation and histological grading, the significance or practical rationale for the use of TF-R in the routine evaluation of benign or malignant oral diseases is unknown. The purpose of the present study is to evaluate the relative expression of TF-R in normal, benign, premalignant and malignant oral mucosa. Specimens of normal mucosa will originate with subjects who need oral surgery for a variety of therapeutic reasons such as alveolectomy, frenectomy or tori removal. Specimens of diseases mucosa will originate with subjects who need surgery for oral chronic keratotic lesions and squamous cells carcinoma. Cryostat sections will be stained by an immunohistochemical method using a murine monoclonal antibody (OKT9) against TF-R. Each section will be examined within five randomly-selected, high-power fields of a light microscope. A total of six anatomic zones (e.g. keratin, prickle cell, granular cell, suprabasal, basal and connective tissue) will be examined. The ratio of TF-R cells to the total number of cells present will be determined. Also, the staining level will be evaluated and will be reported as a range of negative (- = <1%) to strongly positive (++++ = 76-100%). The relationship between lesion type, the ratio of stained to non-stained cells and the degree of staining at each anatomic zone will be analyzed with a factorial analysis of variance and the Tukey Studentized Range Statistic for post hoc purposes. The result from the study will help to determine whether TF-R expression provides a valid marker to discriminate among normal, benign, premalignant and malignant oral mucosa.